855 T5 A/T - Lurching sometimes into P + other automatic questions

[mclovin5891]

Hi all,

I've just picked up a beautiful example of an 855 T5, in Pewter Silver. Currently getting it to full stage 0. Seems like it already has a tune on it so also out to track down what tune it is + pop it on a dyno.

I'm dealing with a lurch into P sometimes. Best way I can describe it is like the rear subframe bonk on the BMW E46s. It doesn't happen all the time, but when it does sometimes the shifter is a bit hard to get into P too. I'm more inclined to believe this to be a problem relating to the transmission mounts or some other rubber/bushing - has anyone had something similar?

On top of that, it seems to roll significantly more before the stopping if I put it in P without the parking brake on. Significantly more as in a good 5-6cm? My 240 is also automatic and does not move anywhere near this much before stopping when in P. Is this normal with the AW50s?

Other than that, the transmission shifts fine, had a flush 40k km ago and changed the oil again, nothing worrying to be seen. It did shift quite harshly into first (again, not all the time, depending on throttle position), but I've noticed it getting much better in the last 1000km or so -
would I be right in putting this down to the tune/gearbox logic adapting from the previous owner (who had a trailer hitch so I assume a caravan of some sort was being towed too). With 316k km however I'm considering getting a box from a junkyard and having it revised just in case the inevitable happens. Any tips/tricks? Places to get parts (EU)?

Thanks!

[Clemens]

One of my 850ies had a problem that sounded similar. I never git around to find the problem and solce it. After 5 or 6 years I retired it (badly worn out oberall condition) and even though the tranny acted up for years, it never broke down.
My meticilously serviced R on the other hand blew up the tranny out of the blue although the AT oil was changed frequently.
What am I trying to tell you? If you want to be on the safe side, try to get a known good transmission as a backup or start harvesting parts for a M56 swap.

The problem is that most of these automatic trannies are way over their life expectancy at this point and there seem to be no parts available nor people who really dig into them besides a solenoid swap.

[hausmeister]

Not sure I understand how it lurches into P? Maybe the locking mechanism is worn out... I'd make sure the Handbrake works good and just live with it, probably. Should not roll that far until it engages.
Could also be worn Transmission/Motor mounts that add to this.

You can also try to get a replacement TCU and swap it in if it makes any difference for the hard shifts. Mine went bad and had all sorts of strange behavior that I thought was normal until I replaced it. It still worked, but not correctly.

My AT is fine so far, but it also not the orig. unit. I have added a trans cooler and do flushes quite often in hope to extend the life.

[wizechatmgr]

I'd recommend using the drain and fill fluid change method going forward. The power flush can and often does stir things up and cause issues.

Have you dropped the pan to check and potentially clean the ATF filter/pickup assembly?

Do you have any stored transmission codes that are currently active? Could be a solenoid that is now full of junk due the power flush.

What did the fluid look like during the last service? Mine came out like chunky chocolate milk and two changes later the transmission is doing great.

[hausmeister]

Have you dropped the pan to check and potentially clean the ATF filter/pickup assembly?

Looking at the trans manuals and diagrams I have I do not believe you can replace the filter without removing and taking the transmission apart. Also the internet/saab forum says it is not a service item.